Pneumocystis carinii (now P. jiroveci)--H&E stain
Typically, foamy, pink exudate fills alveoli. There is little alveolar wall inflammation. Variant histologic patterns have granulomas, cysts, fibrosis, lymphoid infiltrates, hyaline membranes, calcifications, or no foamy exudate.
Pneumocystis carinii (P. jiroveci)--Giemsa stain
A Giemsa stain for trophic forms (formerly called trophozoites) shows dot-like nuclei and pale blue cytoplasm (right arrow). The spore cases (formerly cysts) do not stain, but the intracystic bodies (formerly sporozoites) do (left arrow). Two alveolar macrophages indicate the relative sizes of organisms and cells.
Pneumocystis carinii (P. jiroveci)--Gomori methenamine silver stain
A GMS stain shows spore cases, 7 µm diameter (RBC size), round or cup-shaped with dots on spore case wall.
See also Case 26